1. Field of This Invention
This invention involves the production of isoxazolo [5,4-b] pyridines.
2. Prior Art
Various processes for the synthesis of isoxazolo [5,4-b] are known. Two of such processes start out with 5-amino-isoxazoles, which are cyclized with .beta.-ketoesters or 1,3-diketones (U.S. Pat. No. 3,381,016) or are reacted with alkoxy methylene malonic or acetic acid esters into enamines and are subsequently subjected by heating in diphenyl ether or polyphosphoric acid to cyclization. [(T. Denzel and H. Hoehn, Arch. Pharmaz. 305, 833 (1972), and W. Janssen and T. Denzel, Arch. Pharmaz. 308, 471 (1975)].
Benzohydroxyamino acid chlorides were used for the first time as starting compounds for the production of isoxazoles by Quilico et al., Rend. ist. lombardo sci. 69, 439 (1936), and Quilico et al., Gazz. chim. ital. 67, 589 (1937), in the case of reaction with .beta.-diketones, .beta.-ketoaldehydes, .beta.-ketoesters, malonic esters, cyano acetic ester and cyano ketones. It is particularly mentioned that the reactions with cyano acetamide and cyano acetic ester lead to 3,4,5-trisubstituted isoxazoles.